Catalytic domain of metazoan phosphoinositide-specific phospholipase C-beta
This subfamily corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 126.96.36.199)-beta isozymes. PI-PLC is a signaling enzyme that hydrolyzes the membrane phospholipids phosphatidylinositol-4,5-bisphosphate (PIP2) to generate two important second messengers in eukaryotic signal transduction cascades, Inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG). InsP3 triggers inflow of calcium from intracellular stores, while DAG, together with calcium, activates protein kinase C, which goes on to phosphorylate other molecules, leading to altered cellular activity. Calcium is required for the catalysis. PLC-beta represents a class of mammalian PI-PLC that has an N-terminal pleckstrin homology (PH) domain, an array of EF hands, a PLC catalytic core domain, a C2 domain, and a unique C-terminal coiled-coil (CT) domain necessary for homodimerization. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. There are four PLC-beta isozymes (1-4). They are activated by the heterotrimeric G protein alpha q subunits through their C2 domain and long C-terminal extension. The beta-gamma subunits of heterotrimeric G proteins are known to activate the PLC-beta2 and -beta3 isozymes only. Aside from four PLC-beta isozymes identified in mammals, some eukaryotic PLC-beta homologs have been classified into this subfamily, such as NorpA and PLC-21 from Drosophila and PLC-beta from turkey, Xenopus, sponge, and hydra.
Comment:Both prokaryotic and eukaryotic PI-PLCs utilize a similar catalytic mechanism, a general base and acid catalysis involving two well conserved histidines. It consists of two steps, a phosphotransfer and a phosphodiesterase reaction.
Structure:2FJU; Homo sapiens phospholipase C beta 2 catalytic site residues - View structure with Cn3D